1. Field of the Invention
The present invention relates to a semiconductor device including power switching elements such as an Insulated Gate Bipolar Transistor (IGBT) and so on and its control circuits.
2. Description of the Background Art
Generally, when a control region such as a circuit element, a well to form a circuit element or the like are formed on a semiconductor substrate in which an IGBT which is a power switching element is formed, a parasitic element is generated. In particular, in case that the circuit element is formed on the IGBT by employing a junction separating technique, it is known that a parasitic thyristor is formed by a substrate forming the IGBT and the circuit region, and when this parasitic thyristor is turned on and a latch-up phenomenon occurs, a problem such as leading up to a breakage of the semiconductor device including the IGBT itself and so on occurs.
It is necessary to take measures to place a protective element and so on to prevent such a latch-up phenomenon of the parasitic thyristor, and there is a semiconductor device disclosed in Japanese Patent Application Laid-Open No. 2002-16245, for example, as to take such measures. Means to prevent the latch-up of the parasitic thyristor by employing a schottky barrier diode is disclosed in this semiconductor device.
In the meantime, there is a case that a circuit to measure a voltage generated when a current minute enough to keep the semiconductor device from performing a driving operation is poured from an input terminal of the semiconductor device and to determine that the input terminal is disconnected in case that this voltage reach a predetermined value is added to detect a condition that the input terminal side of the semiconductor device is disconnected in a circuit side driving the semiconductor device including the IGBT composed as described above from outside. Besides, the driving operation of the semiconductor device means an operation of the semiconductor device controlling a conduction/non-conduction between an output terminal and a reference terminal on the basis of a voltage obtained from the input terminal. That is to say, it means that the output terminal and the reference terminal are disconnected with each other (in OFF state) in case that a difference voltage generated between the reference terminal and the input terminal is smaller than a predetermined value, and the output terminal and the reference terminal are connected with each other (in ON state) in case that the difference voltage described above is larger than the predetermined value.
A means such as pulling up by a resistance having a large resistance value (several tens of kΩ, for example) is employed as a means of generating the minute current described above. The voltage obtained by pouring the minute current from the input terminal of the semiconductor device is greatly influenced by an input impedance of the semiconductor device, thus an improvement in an accuracy of the input impedance is required.
A means of providing a resistance in parallel with a control circuit formed in the semiconductor device and so on between the input terminal and the reference terminal (ground terminal) in the semiconductor device is considered as a means of improving the accuracy of the input impedance, for example. At this moment, in case that a resistance such as a polysilicon resistance and so on which can be formed on the semiconductor substrate is employed to control a generation of the parasitic element effectively, it is difficult to form the resistance with higher accuracy because of a change depending on an ambient temperature and an influence of a manufacturing variation and so on.
In this manner, there is a problem in the semiconductor device including the conventional power switching element that the improvement in the accuracy of the input impedance cannot be performed effectively.